There are two types of sensing circuits for touch screens: active type and passive type. An active sensing circuit detects touch points based on high frequency radiation and resonance principles. Typically in an active sensing circuit, multiple inductance coils are set in a sensing board and a controlling board selects one of the inductance coils and delivers alternative current to the selected inductance coil. The inductance coil is actuated by the alternative current to generate magnetic field. Thereafter, when an electronic pen is brought close to the magnetic field, resonance circuit of the electronic pen stores electric energy. After the electric energy is stored in the electronic pen, the controlling board stops delivering alternative current to the selected inductance coil. Meanwhile, resonance circuit of the electronic pen transforms the electric energy to signals by free oscillation. The sensing board converts the signals to electric signals to determine the touch point.
A passive sensing circuit, on the other hand, accumulates charges on a sensing board to make the voltage meet the requirement of a successive circuit. Touch point, in such a case, can be detected based on the voltage.
However, there are certain disadvantages of the above described active and passive sensing circuits. As for an active sensing circuit, in order to accurately determine a touch point, sensing board needs high precision inductance coils. Further, because the signals are weak, the successive circuit is complicated, which increases the production cost. As for the passive sensing circuit, the successive circuit needs to wait a long time for processing the voltage, thereby extending the reactive time of the passive sensing circuit. In some cases, supplemental circuits are used to decrease the reactive time of the passive sensing circuit, however, in such cases the production cost is increased.